//===================================================================================
// Microsoft patterns & practices
// Composite Application Guidance for Windows Presentation Foundation and Silverlight
//===================================================================================
// Copyright (c) Microsoft Corporation.  All rights reserved.
// THIS CODE AND INFORMATION IS PROVIDED "AS IS" WITHOUT WARRANTY
// OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING BUT NOT
// LIMITED TO THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
// FITNESS FOR A PARTICULAR PURPOSE.
//===================================================================================
// The example companies, organizations, products, domain names,
// e-mail addresses, logos, people, places, and events depicted
// herein are fictitious.  No association with any real company,
// organization, product, domain name, email address, logo, person,
// places, or events is intended or should be inferred.
//===================================================================================
using System;
using System.Globalization;
using Microsoft.Practices.Prism.Properties;

namespace Microsoft.Practices.Prism.Events
{
	/// <summary>
	/// Provides a way to retrieve a <see cref="Delegate"/> to execute an action depending
	/// on the value of a second filter predicate that returns true if the action should execute.
	/// </summary>
	/// <typeparam name="TPayload">The type to use for the generic <see cref="System.Action{TPayload}"/> and <see cref="Predicate{TPayload}"/> types.</typeparam>
	public class EventSubscription<TPayload> : IEventSubscription
	{
		private readonly IDelegateReference _actionReference;
		private readonly IDelegateReference _filterReference;

		///<summary>
		/// Creates a new instance of <see cref="EventSubscription{TPayload}"/>.
		///</summary>
		///<param name="actionReference">A reference to a delegate of type <see cref="System.Action{TPayload}"/>.</param>
		///<param name="filterReference">A reference to a delegate of type <see cref="Predicate{TPayload}"/>.</param>
		///<exception cref="ArgumentNullException">When <paramref name="actionReference"/> or <see paramref="filterReference"/> are <see langword="null" />.</exception>
		///<exception cref="ArgumentException">When the target of <paramref name="actionReference"/> is not of type <see cref="System.Action{TPayload}"/>,
		///or the target of <paramref name="filterReference"/> is not of type <see cref="Predicate{TPayload}"/>.</exception>
		public EventSubscription(IDelegateReference actionReference, IDelegateReference filterReference)
		{
			if (actionReference == null)
				throw new ArgumentNullException("actionReference");
			if (!(actionReference.Target is Action<TPayload>))
				throw new ArgumentException(String.Format(CultureInfo.CurrentCulture, Resources.InvalidDelegateRerefenceTypeException, typeof(Action<TPayload>).FullName), "actionReference");

			if (filterReference == null)
				throw new ArgumentNullException("filterReference");
			if (!(filterReference.Target is Predicate<TPayload>))
				throw new ArgumentException(String.Format(CultureInfo.CurrentCulture, Resources.InvalidDelegateRerefenceTypeException, typeof(Predicate<TPayload>).FullName), "filterReference");

			_actionReference = actionReference;
			_filterReference = filterReference;
		}

		/// <summary>
		/// Gets the target <see cref="System.Action{T}"/> that is referenced by the <see cref="IDelegateReference"/>.
		/// </summary>
		/// <value>An <see cref="System.Action{T}"/> or <see langword="null" /> if the referenced target is not alive.</value>
		public Action<TPayload> Action
		{
			get { return (Action<TPayload>)_actionReference.Target; }
		}

		/// <summary>
		/// Gets the target <see cref="Predicate{T}"/> that is referenced by the <see cref="IDelegateReference"/>.
		/// </summary>
		/// <value>An <see cref="Predicate{T}"/> or <see langword="null" /> if the referenced target is not alive.</value>
		public Predicate<TPayload> Filter
		{
			get { return (Predicate<TPayload>)_filterReference.Target; }
		}

		/// <summary>
		/// Gets or sets a <see cref="Events.SubscriptionToken"/> that identifies this <see cref="IEventSubscription"/>.
		/// </summary>
		/// <value>A token that identifies this <see cref="IEventSubscription"/>.</value>
		public SubscriptionToken SubscriptionToken { get; set; }

		/// <summary>
		/// Gets the execution strategy to publish this event.
		/// </summary>
		/// <returns>An <see cref="System.Action{T}"/> with the execution strategy, or <see langword="null" /> if the <see cref="IEventSubscription"/> is no longer valid.</returns>
		/// <remarks>
		/// If <see cref="Action"/> or <see cref="Filter"/> are no longer valid because they were
		/// garbage collected, this method will return <see langword="null" />.
		/// Otherwise it will return a delegate that evaluates the <see cref="Filter"/> and if it
		/// returns <see langword="true" /> will then call <see cref="InvokeAction"/>. The returned
		/// delegate holds hard references to the <see cref="Action"/> and <see cref="Filter"/> target
		/// <see cref="Delegate">delegates</see>. As long as the returned delegate is not garbage collected,
		/// the <see cref="Action"/> and <see cref="Filter"/> references delegates won't get collected either.
		/// </remarks>
		public virtual Action<object[]> GetExecutionStrategy()
		{
			Action<TPayload> action = this.Action;
			Predicate<TPayload> filter = this.Filter;
			if (action != null && filter != null)
			{
				return arguments =>
						   {
							   TPayload argument = default(TPayload);
							   if (arguments != null && arguments.Length > 0 && arguments[0] != null)
							   {
								   argument = (TPayload)arguments[0];
							   }
							   if (filter(argument))
							   {
								   InvokeAction(action, argument);
							   }
						   };
			}
			return null;
		}

		/// <summary>
		/// Invokes the specified <see cref="System.Action{TPayload}"/> synchronously when not overriden.
		/// </summary>
		/// <param name="action">The action to execute.</param>
		/// <param name="argument">The payload to pass <paramref name="action"/> while invoking it.</param>
		/// <exception cref="ArgumentNullException">An <see cref="ArgumentNullException"/> is thrown if <paramref name="action"/> is null.</exception>
		public virtual void InvokeAction(Action<TPayload> action, TPayload argument)
		{
			if (action == null) throw new System.ArgumentNullException("action");

			action(argument);
		}
	}
}